From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 51CFD6FA0 for ; Mon, 16 Jan 2023 16:55:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CAA07C433EF; Mon, 16 Jan 2023 16:55:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1673888150; bh=O/9tsFI4emxdDNgtibqOCVKxzNGTpK0JznlLJKRUlIM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xFFnPmfhrVKJQUcNkLkUC0UUFJaObBXHtb5R+vK/Tkrwtcajt2/Yte7RfyyY/mmgY yBSeK9W2dLRhO+5PcDGGcImBqynsMEUzgWeGnksi81ubwCfQrgNGXPoKy5Xz9c2xgL zlvT3HB1l9CR3YuId1MEqLtJd/2MyrLyJkgV8lIQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Hyunwoo Kim , Takashi Iwai , Hans Verkuil Subject: [PATCH 4.19 392/521] media: dvb-core: Fix UAF due to refcount races at releasing Date: Mon, 16 Jan 2023 16:50:54 +0100 Message-Id: <20230116154904.649093108@linuxfoundation.org> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230116154847.246743274@linuxfoundation.org> References: <20230116154847.246743274@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Takashi Iwai commit fd3d91ab1c6ab0628fe642dd570b56302c30a792 upstream. The dvb-core tries to sync the releases of opened files at dvb_dmxdev_release() with two refcounts: dvbdev->users and dvr_dvbdev->users. A problem is present in those two syncs: when yet another dvb_demux_open() is called during those sync waits, dvb_demux_open() continues to process even if the device is being closed. This includes the increment of the former refcount, resulting in the leftover refcount after the sync of the latter refcount at dvb_dmxdev_release(). It ends up with use-after-free, since the function believes that all usages were gone and releases the resources. This patch addresses the problem by adding the check of dmxdev->exit flag at dvb_demux_open(), just like dvb_dvr_open() already does. With the exit flag check, the second call of dvb_demux_open() fails, hence the further corruption can be avoided. Also for avoiding the races of the dmxdev->exit flag reference, this patch serializes the dmxdev->exit set up and the sync waits with the dmxdev->mutex lock at dvb_dmxdev_release(). Without the mutex lock, dvb_demux_open() (or dvb_dvr_open()) may run concurrently with dvb_dmxdev_release(), which allows to skip the exit flag check and continue the open process that is being closed. CVE-2022-41218 is assigned to those bugs above. Reported-by: Hyunwoo Kim Cc: Link: https://lore.kernel.org/20220908132754.30532-1-tiwai@suse.de Signed-off-by: Takashi Iwai Signed-off-by: Hans Verkuil Signed-off-by: Greg Kroah-Hartman --- drivers/media/dvb-core/dmxdev.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/drivers/media/dvb-core/dmxdev.c +++ b/drivers/media/dvb-core/dmxdev.c @@ -800,6 +800,11 @@ static int dvb_demux_open(struct inode * if (mutex_lock_interruptible(&dmxdev->mutex)) return -ERESTARTSYS; + if (dmxdev->exit) { + mutex_unlock(&dmxdev->mutex); + return -ENODEV; + } + for (i = 0; i < dmxdev->filternum; i++) if (dmxdev->filter[i].state == DMXDEV_STATE_FREE) break; @@ -1457,7 +1462,10 @@ EXPORT_SYMBOL(dvb_dmxdev_init); void dvb_dmxdev_release(struct dmxdev *dmxdev) { + mutex_lock(&dmxdev->mutex); dmxdev->exit = 1; + mutex_unlock(&dmxdev->mutex); + if (dmxdev->dvbdev->users > 1) { wait_event(dmxdev->dvbdev->wait_queue, dmxdev->dvbdev->users == 1);